Graduate School of Engineering, Hokkaido University, N13W8, Sapporo 060-8628, Japan.
Water Sci Technol. 2010;62(11):2579-89. doi: 10.2166/wst.2010.540.
We quantitatively evaluated the factors that affect the concentrations of rice-farming pesticides (an herbicide and a fungicide) in river water by a sensitivity analysis using a diffuse pollution hydrologic model. Pesticide degradation and adsorption in paddy soil affected concentrations of the herbicide pretilachlor but did not affect concentrations of the fungicide isoprothiolane. We attributed this difference to the timing of pesticide application in relation to irrigation and drainage of the rice paddy fields. The herbicide was applied more than a month before water drainage of the fields and runoff was gradual over a long period of time, whereas the fungicide was applied shortly before drainage and runoff was rapid. However, the effects of degradability-in-water on the herbicide and fungicide concentrations were similar, with concentrations decreasing only when the rate constant of degradation in water was large. We also evaluated the effects of intermittent irrigation methods (irrigation/artificial drainage or irrigation/percolation) on pesticide concentrations in river water. The runoff of the fungicide, which is applied near or in the period of intermittent irrigation, notably decreased when the method of irrigation/artificial drainage was changed to irrigation/percolation. In a sensitivity analysis evaluating the synergy effect of degradation and adsorbability in soil, the degradation rate constant in soil greatly affected pesticide concentration when the adsorption coefficient was small but did not affect pesticide concentration when the adsorption coefficient was large. The pesticide concentration in the river water substantially decreased when either or both the degradation rate constant in soil and adsorption coefficient was large.
我们通过使用漫射污染水文学模型进行敏感性分析，定量评估了影响河水中稻田农药（一种除草剂和一种杀菌剂）浓度的因素。在稻田土壤中，农药的降解和吸附会影响除草剂丙草胺的浓度，但不会影响杀菌剂异噻菌胺的浓度。我们将这种差异归因于农药在与稻田灌溉和排水相关的时间上的应用。除草剂在排水前一个多月就已施用于田地，而径流则在很长一段时间内逐渐增加，而杀菌剂则在排水前很短的时间内施用于田地，并且径流很快。然而，水中降解性对除草剂和杀菌剂浓度的影响相似，只有当水中降解的速率常数较大时，浓度才会降低。我们还评估了间歇性灌溉方法（灌溉/人工排水或灌溉/渗滤）对河水中农药浓度的影响。当将灌溉/人工排水方法更改为灌溉/渗滤时，靠近或在间歇性灌溉期间施用的杀菌剂的径流明显减少。在评估土壤中降解和吸附协同作用的敏感性分析中，当土壤的吸附系数较小时，土壤中降解的速率常数会极大地影响农药浓度，但当吸附系数较大时，土壤中降解的速率常数不会影响农药浓度。当土壤中降解的速率常数或吸附系数较大时，河水中的农药浓度会大大降低。
